ABB RELION RET670 Applications Manual page 352

Section 8
Impedance protection
346
matter. Phase selection, quadrilateral characteristic with settable angle (FRPSPDIS, 21)
is designed to accurately select the proper fault loop in the distance measuring function
depending on the fault type.
The heavy load transfer that is common in many transmission networks may in some
cases be in opposite to the wanted fault resistance coverage. Therefore, the function
has a built in algorithm for load encroachment, which gives the possibility to enlarge
the resistive setting of both the Phase selection with load encroachment and the
measuring zones without interfering with the load.
A current-based phase selection is also included. The measuring elements continuously
measure three phase currents and the residual current and, compare them with the set
values.
The extensive output signals from FRPSPDIS (21) give also important information
about faulty phase(s), which can be used for fault analysis.
Load encroachment
Each of the six measuring loops has its own load (encroachment) characteristic based
on the corresponding loop impedance. The load encroachment functionality is always
active, but can be switched off by selecting a high setting.
The outline of the characteristic is presented in figure 162. As illustrated, the resistive
blinders are set individually in forward and reverse direction while the angle of the
sector is the same in all four quadrants.
1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual